Managing brush and maintaining habitat for endangered species

Abstract: This paper presents brush management guidance for selected wildlife species that are either federally or state listed as endangered or threatened or are considered species of concern in Texas. The recommendations presented here concerning federally-listed species are the result of consultations between Texas Parks and Wildlife Department and the U.S. Fish and Wildlife Service. Landowners who carry out brush management practices within these guidelines can be assured, with the greatest certainty possible, that they would not be in violation of the federal Endangered Species Act.

In planning a brush management program, it is important to realize that different kinds of wildlife have different habitat needs. Some species inhabit grasslands, others shrublands, and still others mature woodland. The amount and type of woody vegetation available to these species affects their ability to find suitable food and cover for survival and reproduction. Rare species are particularly vulnerable, often because of threats associated with habitat loss, fragmentation of suitable habitat, or alteration of habitats from human activities. Many rare species have very specific habitat requirements or restricted ranges. With knowledge of their basic life history and habitat requirements, landowners can manage their land in ways that support rare species while still achieving overall management and economic goals. Habitat conservation and enhancement for rare species can be built into your overall ranch management plan, and for many species, it may be easier than you think.

The purpose of this paper is to provide landowners and managers with guidance concerning brush management activities and their effects on rare species. It is not our purpose to provide a complete analysis of what is known concerning how manipulation of woody vegetation affects all species considered rare in Texas. Rather, we will concentrate on presenting brush management guidance for selected species that are either federally or state listed as endangered or threatened or are considered species of concern in Texas. The recommendations presented here concerning federally listed species are the result of consultations between Texas Parks and Wildlife Department and the U.S. Fish and Wildlife Service. Landowners who carry out brush management practices within these guidelines can be assured, with the greatest certainty possible, that they would not be in violation of the federal Endangered Species Act.

Woodland species

Golden-cheeked Warbler (federally listed as endangered). The golden-cheeked warbler is a migratory songbird that nests in the mature juniper-oak woodlands of central Texas (Edwards Plateau) and winters in the pine-oak woodlands of southern Mexico and central America. Typical nesting habitat is found in tall, dense, mature stands of Ashe juniper (blueberry cedar) mixed with trees such as Texas (Spanish) oak, Lacey oak, Durand (scalybark) oak, plateau live oak, post oak, Texas ash, cedar elm, hackberry, bigtooth maple, sycamore, Arizona walnut, escarpment cherry, and pecan. This type of woodland generally grows in relatively moist areas such as steep-sided canyons and slopes. A mix of juniper and deciduous trees on the slopes, along drainage bottoms, and in creeks and draws provide an ideal mix of vegetation for these birds.

Golden-cheeked warblers feed almost entirely on caterpillars, spiders, beetles, and other insects found in foliage of the tree canopy. The birds build a small cup-shaped nest out of fine strips of juniper bark woven together with spider webs. The presence of some mature juniper trees with shredding bark is considered an essential component of the habitat.

Since golden-cheeked warblers inhabit wood-lands, usually with 50% or more canopy cover of juniper and hardwood trees, disturbances to the tree canopy should be avoided when planning brush management activities in or adjacent to golden-cheeked warbler habitat. Dozing or hand-cutting in habitat with closed tree canopy and steep slopes not only destroys warbler habitat, but mechanical disturbance also can create serious soil erosion problems. In addition, clearing these areas is generally not cost effective due to higher clearing costs, lower forage production potential, and grazing distribution problems associated with steep slopes. Selective removal of young “bushy” juniper less than 10 feet in height within habitat is not a problem as long as the tree canopy is not disturbed. Any selective removal of juniper within or adjacent to habitat should be done during the non-nesting period (September-February).

When mature juniper trees are abundant in the habitat, incidental removal of juniper for use as fenceposts will have little impact on warbler habitat. The number of trees cut depends on the density of Ashe juniper in the habitat. For example, more trees could be removed from an area with a high density of juniper compared with the density of hardwoods. The idea should always be to provide a mix of juniper and hardwoods. When posting is done, trees should be selected to avoid disturbance to the tree canopy. One way to do this is to select trees with a relatively small individual canopy and scatter your tree selections over the area. Posting should not occur in habitat during the nesting period (March-August).

The above discussion concerns brush management within golden-cheeked warbler habitat. A complete discussion of what is and what is not considered habitat can be found in Campbell (1995).

Considering the current interest in economic opportunities related to nature-based tourism (particularly birdwatching) in Texas, there may be some cases where landowners want to restore or create habitat for the golden-cheeked warbler in areas that currently do not support them. One type of restorable habitat is the relatively mesic (moist) area, with a diversity of deciduous trees, where junipers have been previously removed. Allowing the reestablishment of juniper on these sites would eventually result in the mature oak-juniper woodland preferred by golden-cheeked warblers.

Other situations where restoring habitat may be a possibility include relatively mesic areas dominated by juniper, where heavy browsing pressure by deer or livestock has prevented the establishment of hardwood seedlings. In these areas, control of deer numbers and planned deferment from livestock grazing would promote reestablishment of broad-leaved shrubs and trees, eventually resulting in a mature juniper-oak woodland.

In mesic areas where small junipers (10 ft. or less) are dominant, small junipers could be thinned to favor faster growth of remaining trees. Thinning would encourage hardwood regeneration, especially if some slash is left in place to provide protection for hardwood seedlings. If large junipers are dominant, several small openings per acre would encourage hardwood regeneration. These openings should be protected from browsing and left to regenerate naturally, or planted to native hardwoods. In each of these examples, the idea is to restore areas that may once have provided habitat to the natural oak-juniper woodland capable of growing on the site.

Shrubland species

Black-capped Vireo (federally listed as endangered). The black-capped vireo is a migratory songbird that breeds in central Texas and winters along the western coast of Mexico. In Texas, vireo habitat is found on rocky limestone soils of the Edwards Plateau, Cross Timbers and Prairies, and eastern Trans-Pecos. Although vireo habitat throughout Texas is highly variable with regard to plant species, soils, temperature, and rainfall, all habitat types are similar in vegetation structure; i.e. the “overall look” is somewhat similar although the plant species vary. Vireos require shrub vegetation reaching to ground level for nesting cover. This low-growing shrub cover is important because most cup-shaped nests are built at about “door-knob” height, or about 3 to 4 feet above the ground.

Black-capped vireos typically nest in shrublands and open woodlands with a distinctive patchy structure. Typical habitat is characterized by shrub vegetation extending from the ground to about 6 feet and covering about 30 to 60 percent of the total area. In the eastern portion of the vireo’s range, the shrub layer is often combined with an open, sparse to moderate tree canopy. Open grassland separates the clumps of shrubs and trees.

In the western Edwards Plateau and Trans-Pecos Regions, on the western edge of the vireo’s range, the birds are often found in canyon bottoms and slopes where sufficient moisture is available to support diverse shrub vegetation. Dominant woody plants in this habitat type include sandpaper oak, vasey shin oak, Texas kidneywood, Mexican walnut, and fragrant ash, mountain laurel, and guajillo.

For all habitat types, the plant composition appears to be less important than the presence of adequate broad-leaved shrubs, foliage to ground level, and mixture of open grassland and woody cover. Deciduous and broad-leaved shrubs and trees throughout the vireo’s range are also important in providing habitat for insects on which the vireo feeds.

Prescribed burning is an excellent management tool to maintain the desired vegetation structure for vireo nesting; i.e. a mosaic of shrubs and open grassland with abundant woody foliage below 6 feet. The use of prescribed burning is especially important in the eastern portion of the vireo’s range, since plant succession often leads to the vegetation becoming too tall and dense to provide good nesting habitat. Cool- season burns, conducted prior to March 15, are often recommended to control small juniper, thus maintaining the relatively open shrublands preferred by vireos. Prescribed burns conducted during late spring and early fall, under hotter conditions, can be used to set back plant succession in order to create vireo habitat; however, warm season burns should be done only in areas that do not currently support black-capped vireos. On grazed rangeland, prescribed burns should be coordinated with livestock rotation to allow for needed deferments.

Desirable burn intervals for cool season burns vary throughout the state, depending on rainfall and vegetation type. Field experience shows that, for much of the Hill Country, a burning interval of 4 to 7 years is considered desirable to keep Ashe juniper (cedar) invasion in check and to allow regrowth of broad-leaved shrubs. Maintaining open grassland areas between clumps of shrubs is important for good vireo habitat.

Fire is a natural component of Texas rangelands, and prescribed burning has many range and wildlife management benefits. These include improved forage quality and availability for livestock and deer, and maintenance of desirable plant composition and structure. Landowners are advised to contact local representatives of the Texas Parks and Wildlife Department, U.S. Natural Resource Conservation Service, or Texas Agricultural Extension Service for help in developing and implementing a prescribed burning program designed specifically for your property and management objectives.

Increases in juniper (cedar) and other woody species can easily cause the vegetation to grow (succeed) out of the patchy, low shrub cover that provides suitable habitat. In the eastern portion of the vireo’s range, good nesting habitat generally has between 30 and 60 percent shrub canopy. Selective brush removal with herbicides or mechanical means can be used to keep the habitat favorable for vireo nesting. For example, the selective removal of juniper, mesquite, or pricklypear (less desirable to the vireo and to the rancher) serves to maintain a relatively open shrub canopy and encourages growth of associated broad-leaved shrubs. Selective brush removal should strive to maintain the low shrubby structure.

When using herbicides, careful attention to the kinds, amounts, timing, and application technique will achieve the best control of target species at minimum cost. Precise application also reduces the risk of environmental contamination and off-site effects. It is best to choose highly selective individual plant treatment methods, whenever practical, to avoid damage to desirable shrubs such as live oak, shin oak, Texas oak, hackberry, Texas persimmon, sumac, redbud, and elm. Herbicides should always be used in strict accordance with label directions, including those for proper storage and disposal of containers and rinse water. Herbicide applications should not occur during the breeding season, except for basal applications or individual plant treatment of prickly pear pads.

Hand-cutting or carefully planned mechanical methods of brush management such as chaining, roller chopping, or shredding can be used to stimulate basal sprouting of key woody species in order to maintain, enhance, or create vireo habitat. Mechanical methods should only be used during the non-breeding season (October-February).

Finally, we want to emphasize the compatibility of producing high quality white-tailed deer, healthy cattle, and thriving populations of black-capped vireos on well-managed rangelands in the Edwards Plateau. A range management program consisting of selective brush management, prescribed fire, and control of deer and livestock grazing pressure will often create a desirable mix of low-growing woody species that not only provides excellent habitat for white-tailed deer and forage for livestock, but also nesting habitat for black-capped vireos.

Ocelot and jaguarundi(both wild cats are federally listed as endangered). In Texas, ocelots and jaguarundis occur in the dense thorny shrublands of the Lower Rio Grande Valley and Rio Grande Plains. Deep, fertile clay or loamy soils are generally needed to produce suitable habitat. Typical habitat consists of mixed brush species such as spiny hackberry, brasil, desert yaupon, wolfberry, lotebush, amargosa, whitebrush, catclaw, blackbrush, lantana, guayacan, cenizo, elbowbush, and Texas persimmon. Inter-spersed trees such as mesquite, live oak, ebony, and hackberry also occur. Although the jaguarundi has not been as well-studied in Texas as the ocelot, researchers believe it has similar habitat requirements.

Canopy cover and density of shrubs are important considerations in identifying suitable habitat. Optimal habitat has at least 95 percent canopy cover of shrubs, whereas marginal habitat has 75 to 95 percent canopy cover. Shrub density below the four foot level is the most important component of ocelot habitat. Shrub density should be such that the depth of vision from outside the brush line is restricted to about five feet. Because of the density of brush below the four foot level, human movement within the brush stand would be restricted to crawling.

Mechanical or chemical brush control, including prescribed burning, should not be conducted in habitat areas or in brushy corridors connecting larger areas of habitat. In everyday agricultural operations (i.e. livestock water facilites, fence construction), it is important to minimize disturbances that would destroy the integrity of a habitat tract or corridor. Tracts of at least 100 acres of isolated brush (of the required density and structure), or 75 acres of brush interconnected with other habitat tracts by brush corridors, are considered important habitat. However, useful habitat can be provided by tracts as small as 5 acres or less.

Where dense mixed brush has developed into a tree form, or shrub density below four feet is inadequate, mechanical brush treatment methods such as chaining or roller chopping may be used to restore or create suitable habitat. These mechanical methods encourage basal sprouting by breaking off limbs or trunks of established plants, and can be used to increase cover and density of brush below the four foot level.

Adapted native shrubs, such as ebony, brasil, and granjeno, can be planted to increase habitat or to provide interconnecting corridors to existing habitat. Methods are currently being developed to allow for more successful establishment of these species.

The reason these cats are so rare is that the extensive shrublands of the Lower Rio Grande Valley have been converted to cropland and urban development over the past 60 years. Much of this land, particularly the more fertile soils, has been cleared for the production of vegetables, citrus, sugarcane, cotton, and other crops. Unfortunately for the cats, the best soil types also grow the thickest brush and thus produce the best habitat. Less than 5 percent of the original vegetation remains.

Maintaining what is left of the dense stands of mixed thornshrub is vital to the survival of these rare cats in Texas. Maintaining habitat around the Laguna Atascosa National Wildlife Refuge, in the Lower Rio Grande Valley, and in counties directly north of this area is particularly important.

Grassland species

Attwater’s prairie chicken. The Attwater’s praire chicken is considered by many to be the most endangered animal in Texas. From more than a million birds at the turn of the century to less than 60 in the wild in 1997, the Attwater’s prairie chicken is very close to extinction. Loss of coastal prairie grasslands, 6 million acres which once stretched from south Texas to western Louisiana, is the problem. Urbanization and industrial development, conversion of rangeland to rice production and introduced grasses, and invasion of brush species on the coastal prairies have all contributed to habitat loss.

Habitat for the Attwater’s prairie chicken consists of open tallgrass coastal prairie dominated by bunchgrasses such as little bluestem, indiangrass, switchgrass, and big bluestem, along with various flowering plants. Preferred habitat is characterized by high plant diversity and variations in grass height. The birds prefer open prairies without any woody cover, and avoid areas with more than 25 percent cover of shrubs. Preferred habitat is also characterized by knolls and ridges, with the minor variations in topography and soils on these sites resulting in a variety of vegetation types.

Prairie chickens feed on a wide variety of plant parts and insects. Potential food sources, both vegetation and insects, vary by season, location, and availability. Studies have shown that green foliage and seeds make up most of the diet, whereas insects are important seasonally. The foliage and seeds of native forbs are particularly important in the diet. Most commonly consumed plants include Ruellia, yellow falsegarlic, upright prairie- coneflower, leavenworth vetch, stargrass, bedstraw, doveweed, and ragweed. Insects make up the majority of the diet of chicks.

Management for Attwater’s prairie chicken involves good grazing management and carefully planned prescribed burning and brush management. Range management practices aimed at achieving and maintaining good and excellent range condition will benefit the prairie chicken, as well as other plants and animals that share its habitat, including livestock.

The coastal tallgrass prairie evolved under the influence of natural and man-caused fires. Prescribed burning, therefore, is an excellent management tool for maintaining healthy grassland and improving prairie chicken habitat. Periodic burning keeps woody plant invasion under control. It also reduces rank growth of vegetation, which is unpalatable for cattle and too dense for prairie chickens. Burned areas are often used for booming grounds, especially if shortgrass areas are in short supply. Prescribed burning also improves plant diversity and, in the case of winter burns, provides succulent food for prairie chickens during the winter and early spring. Prescribed burning should be completed by late February.

Mechanical or chemical brush management techniques are often needed to provide initial control in areas of dense, large brush. Prescribed burning is not an option in many of these areas because there is not enough grass to carry the fire or brush is too large to be effectively controlled by fire. Each brush problem is unique, and technical assistance from knowledgeable people is helpful. Factors such as type, density and size of target species, range site and soils, past history of brush management, and surrounding land use must be considered.

The right kinds, amounts, and application techniques for herbicide treatments are important in achieving good control of target species. Many herbicides are very selective, so choosing the correct formulation of one or more herbicides is very important for successful treatment of a particular brush problem. In some cases, timing of application can make the difference between good and poor results. Using the most precise and selective herbicide treatment also saves money, reduces the risk of environmental contamination, and reduces the chances of affecting desirable food plants (i.e. seed-producing forbs).

Combining methods of brush management, such as herbicide or mechanical control and prescribed burning, is often very effective. For example, on rangeland infested with Macartney rose, herbicide application followed by periodic prescribed burning can provide good results in reducing brush and restoring grassland. Mechanical methods such as dozing, roller chopping, or shredding can be followed by prescribed burning or herbicide application, depending on the target species. Prescriptions need to be carefully designed to achieve the best results at the lowest cost. As with any range management practice, good grazing management (i.e. proper stocking and rotational grazing) is vital to achieving cost effective treatment and improvement in range condition.

Northern Aplomado falcon(federally listed as endangered). The northern subspecies of the Aplomado falcon once inhabited grassland, savannah, and desert scrub areas throughout parts of southern Texas, New Mexico, and Arizona, and southward through Mexico to the western coast of Guatemala. In the United States, the Aplomado falcon was regularly seen on the coastal prairies of south Texas.

Aplomado falcon habitat consists of open grassland with scattered trees or shrubs. In the past, Aplomados were most abundant in the coastal grasslands of south Texas and the savannah grasslands of eastern Mexico. These birds also inhabited coastal dunes and tidal flats, and margins of inland marshes and riparian woodlands. Occupied habitat in Mexico has been described as having tree densities of about 19 trees per 100 acres, an average distance between trees of about 100 feet, and average tree height of 30 feet.

Scientists believe that before the turn of the century, Aplomado falcons were quite common in the grasslands of southern and western Texas, New Mexico, and Arizona. Several pioneer naturalists wrote that they frequently saw this species in their travels. By the 1930s, the Aplomado falcon had become very rare in the United States. The last nesting pair reported in Texas was in Brooks County in 1941, and the last confirmed nest within the United States was in New Mexico in 1952. On the King Ranch in south Texas in 1949, Val Lehmann collected the last Aplomado falcon specimen from the United States. He continued to see Aplomados in this area until the 1950s. Today, Aplomado falcons can once again be seen in south Texas, thanks to a cooperative reintroduction program between The Peregrine Fund, Inc., the U.S. Fish and Wildlife Service, and private landowners.

Brush encroachment resulting from uncontrolled livestock grazing and fire suppression has altered much of the grassland habitat once inhabited by Aplomado falcons in Texas. Continuous heavy grazing pressure, which reduces plant diversity and leads to declines in range condition and brush invasion, affects Aplomado falcons by reducing habitat for prey species. Aplomado falcons tend to abandon nesting territories where grass ground cover gives way to brush.

Well-planned brush management and periodic prescribed burning are management practices that can be used to maintain open rangelands with scattered mottes of brush and trees, which is preferred habitat for Aplomado falcons. Management for these falcons is therefore very compatible with practices that maintain and restore healthy rangelands. In fact, the presence of Aplomado falcons often reflects good rangeland management. Well-managed pastures with a diversity of perennial grass and substantial ground cover are likely areas for these falcons. Grazing management (moderate stocking, rotational grazing), selective brush control, range seeding, and prescribed fire can be used to maintain diverse and productive rangelands able to support abundant prey for Aplomado falcons.

Lesser prairie chicken(not listed, considered species of concern in Texas). Historically, the Lesser prairie chicken inhabited large blocks of native rangeland in the High and Rolling Plains. Habitat on the High Plains consisted of short grasses on clay loam soils along with shinoak, sand sagebrush, and a mixture of warm season perennial bunchgrasses on the interspersed sandy soils. On the Rolling Plains, bunchgrasses were dominant on the sandy loam soils, with shinoak associations on the sands. Much of the habitat in the High Plains has been converted to cropland, with only the sand-shinnery associations remaining to provide habitat. Although less extensive, similar habitat alteration has occurred in the Rolling Plains. Encroachment of tall brush such as mesquite and juniper has caused habitat loss in the southeastern Panhandle. Although prairie chickens need low brush for screening and thermal cover, tall brush provides cover for predators, overruns lek sites, and interferes with the bird’s flush. Even though the Conservation Reserve Program holds promise for restoring prairie chicken habitat, many acres of CRP have been planted in less desirable, non-native plants and grass monocultures, which may provide cover but produce little food and thus are poor brood rearing habitats.

Like the Attwater’s prairie chicken on coastal grasslands, the lesser prairie chicken is a species dependent on large areas of high quality, well-managed rangelands. Proper stocking, rotational grazing, and periodic prescribed burning are recommended to improve range condition, increase plant diversity, and enhance habitat for lesser prairie chickens. Since these birds eat shinoak acorns along with a variety of grass and forb seeds, leaves, and fruits, it is important to maintain a variety of plants in the habitat. Early successional forbs for food, climax tall and mid-height bunchgrasses for nesting cover, and low brush for screening cover are all important.

Lesser prairie chickens benefit from a mosaic pattern of shinoak mottes within stands of tall and mid-height grasses. The goal of habitat management should be to maintain rangeland in good to excellent condition, with a diversity of grasses and forbs interspersed with low-growing woody cover. Grazing systems which maintain mid-successional to climax grasses and which leave adequate residual cover would benefit lesser prairie chickens; thus rotation, deferment, or moderate use of rangeland is required (Taylor and Guthery 1980). When using herbicides, keep in mind that forbs are very important in the diet of these birds, so it is best to choose a treatment that selectively controls the brush without unduly affecting the food supply. The following brush management recommendations are from Litton et. al. 1994:

(1) Don’t treat the same areas with herbicide in yearly repetition. Periodic treatments will allow forb and brush regrowth to provide necessary food and cover for birds while maintaining the desired level of brush.

(2) When treating large areas, leave untreated strips wide enough to provide areas of desirable food production and cover next to treated areas.

(3) On larger ranches, a rotation method of brush management can be used so that portions of different pastures may be treated each year maintaining an interval of 6 to 8 years for various untreated pastures.

(4) It is most desirable to leave mature, taller-growing shinoak mottes. Although this requires extra care, these mottes are very important to prairie chickens and many other wildlife species. Also, destruction of mottes on deep sand sites encourages severe wind erosion or “blowouts”.

(5) Prescribed burning in late winter/early spring can be used to enhance native grass nesting cover and encourage production of native foods (forbs, insects, young green growth). For best results, adequate soil moisture before and after the burn is needed. Landowners are encouraged to prepare a prescribed burning plan with help from one of the technical assistance agencies.

Other species of concern

White-tailed hawk(state listed as threatened). Inhabits open to semi-open grassland or savannah on the Coastal Prairie of Texas. Preferred habitat consists of scattered tall shrubs (yucca, mesquite, granjeno, spiny hackberry) covering 0 to 40 percent of the total area. Brush management considerations should include maintaining an open rangeland or savannah with scattered brush and a diversity of plants, providing habitat for a wide variety of prey species (small vertebrates and arthropods).

Texas Botteri’s sparrow(state listed as threatened).

Another species dependent upon high quality Coastal Prairie grasslands and savannahs. Habitat consists of tall bunchgrasses with widely scattered mesquite, huisache, and yucca located within about 20 miles of the Gulf of Mexico. Management practices that maintain good to excellent range condition will benefit this species.

Baird’s sparrow (not listed, considered species of concern). This migratory winter resident inhabits grasslands and savannahs and has been seen in scattered locations throughout the state. Little is known about the winter distribution or habitat requirements of this species in Texas. Encouraging the conservation of native rangelands is considered an important management need.

Henslow’s sparrow (not listed, considered species of concern). This species is a winter resident in the Pineywoods and Gulf Coastal Prairie regions. Its decline is directly related to loss of tallgrass coastal prairie rangelands. Beneficial management includes prairie restoration along with careful grazing management and periodic burning to prevent woody plant invasion. In the Pineywoods, management to maintain a mature pine savannah with a dense herbaceous layer would benefit this species.

Contact

AgriLife Bookstore

AgriLife Extension's online Bookstore offers educational information and resources related to our many areas of expertise and programming; from agriculture, horticulture, and natural resources to nutrition, wellness for families and youth, and much more.